With incessant industrial development, an increasing number of power line networks are being set-up in rural as well as forest areas. These power line networks often include overhead power lines that need to be monitored from time to time to maintain adequate clearance between their energized conductors and the ground beneath the power lines. Moreover, it is desirable that the power line networks be resilient to storms, earthquakes and other potential causes of damage, so as to be able to meet increasing power demands at all times.
However, encroaching vegetation, such as a tree growing in proximity of a power line, pose potential threats to the power line. In one example, the tree might grow taller than the power line over a period of time. During a storm, the tree might fall over the power line, thereby breaking the power line and leading to a power failure. In another example, a branch of the tree might grow above the power line. During a snow fall, the branch might bend over the power line, due to heavy load of snow collected over the branch. This may lead to a problem in the power line, as the branch of the tree is in direct contact with the power line. Therefore, it is desirable that an accurate monitoring of the power line be performed from time to time, to mitigate risks posed by the encroaching vegetation and other objects, such as man-made structures and buildings.
Moreover, in case of a natural disaster, such as a major storm, a substantial amount of damage may occur to the power line. This may lead to massive disruption to power transmission and distribution. In such a case, a quick and accurate analysis of the damage is of utmost importance for power transmission and distribution operators, so as to enable them to manage repair work efficiently.
Traditionally, power lines have been monitored by on-site manual inspection. Such manual inspection often provides inaccurate results, as it is ground-based and is unable to cover upper structures of power pylons and/or crowns of trees. Moreover, manual inspection is expensive and time-consuming.
Some conventional systems for monitoring a power line network employ Light Detection And Ranging (LiDAR) system for generating three-dimensional models of the power line network and objects in a proximity of the power line network. A typical scanning LiDAR system consists of (1) a laser ranging unit (i.e. LiDAR) (2) an opto-mechanical scanner, (3) a position and orientation unit, and (4) a control, processing and storage unit. The laser ranging unit can be subdivided into a transmitter, a receiver, and the optics for both units. The receiver is a photodiode, which converts the incident power received by the detector to a current at the output. The receiver optics collects the backscattered light and focuses it onto the detector, which converts the photons to electrical impulses. The opto-mechanical scanning unit is responsible for the deflection of the transmitted laser beams across the flight path. The design of the deflection unit (e.g. oscillating mirror/zig-zag scanning, rotating mirror/line scanning, pushbroom/fiber scanning, Palmer/conical scanning) defines the scan pattern on the ground. A differential GNSS receiver provides the position of the laser ranging unit. Its orientation is determined by the pitch, roll, and heading of the aircraft, which are measured by an inertial navigation systems. Airborne LiDAR, i.e. Airborne Laser Scanning (ALS) is a method based on Light Detection and Ranging (LiDAR) measurements from an aircraft, where the precise position and orientation of the sensor is known, and therefore the position (x, y, z) of the reflecting objects can be determined. In addition to ALS, there is an increasing interest in Terrestrial Laser Scanning (TLS), where the laser scanner is mounted on a tripod or even on a moving platform, i.e. Mobile Laser Scanning (MLS)/Mobile LiDAR.
In one such conventional system, a helicopter is used to carry a LiDAR unit over the power line network. The LIDAR unit is operable to emit radiation beams that reflect from the objects and return to the LiDAR unit. For this purpose, the LiDAR unit may use ultraviolet, visible, or near infrared radiation. The LiDAR unit is then operable to measure a time taken by the emitted beams to return, and determine distances to the objects.
Additionally, an airborne system can also take digital images to which a photogrammetric process can be applied. The aim of photogrammetry is to make images measurable, i.e. to determine the position (X, Y, and Z) and the rotation angles (omega, phi, and kappa) of the camera, and to make measurements from the image. One of the most important applications of photogrammetry has been topographic mapping. The photogrammetric process from planning, image acquisition and orientation to 3D surface reconstruction has been nearly completely automated. Automatic digital image matching techniques (also called dense matching), such as cross correlation, SIFT, and Semi-Global Matching, are used or creating 3D models of the target area. However, the basic aim of photogrammetry is still the same that is, to determine the orientations of images and to make measurement (3D data) from the visible environment. Today photogrammetry can provide a point cloud having x, y, z coordinates similarly to LiDAR by using overlapping images and automated digital image matching processing.
However, the conventional systems suffer from several disadvantages. Firstly, a trained pilot is required to fly the helicopter over the power line network. Secondly, a human operator is required to operate the LiDAR unit from the helicopter. Thirdly, significant amount of fuel and time is consumed, making the whole system very expensive. Fourthly, in case of a major natural disaster, such as a thunder storm or a hurricane, the helicopter may be prevented from flying due to aviation regulations and safety. This means that the conventional systems cannot be used at a time when LiDAR measurements are needed most urgently.
Therefore, there exists a need for a system for monitoring power lines that is capable of detecting potential threats to the power lines, even during a major natural disaster.